IRI Climate Information Digest - December 1999

Issued 13 January 2000

October-December 1999 Precipitation Percent
of Average

Climatological Background

In December, the Northern Hemisphere enters the heart
of winter, with strong north-south temperature differences driving the
mid-latitude jet stream and storm systems. In the Southern
Hemisphere summer is under way, with monsoon systems gaining strength
in South America, southern Africa, and Australia.

Ocean Temperatures

Tropics: In the tropical Pacific Ocean, La
Niña (below average sea surface temperatures (SSTs) in the
equatorial Pacific) has continued to strengthen in the central part of
the basin. However, most models are predicting this event to begin weaking
through March.

Extratropics: Above average SSTs continue
to persist in a broad band extending from Japan to the west-central North
Pacific. Warmer than average SSTs strengthened to the west of Australia
and along the west coast and southern tip of Africa.

Land Temperatures

Australia: Colder than average temperatures
occurred in Queensland and parts of Western Australia.

South America: Warmer than average temperatures
prevailed in the region of the Guyanas and through much of eastern Brazil
with differences up to 2 degrees C above average.

Africa: Much of Africa reported temperatures
up to 2 degrees C above average.

Europe and Asia: Central Asia and the
Middle East experienced above average temperatures, with differences exceeding
6 degrees C east of the Ural Mountains.

North America: Most of Canada and the
northern and central United States were warmer than average, with differences
exceeding 6 degrees C in Saskatchewan, Alberta and Quebec.

Precipitation: October-December

Australia and Southeast Asia: Above
average rainfall fell in Queensland and Western Australia marking
an early start to the Australasian monsoon. Tropical storm activity
resulted in above average rainfall in Vietnam.

South America: While Venezuela and the
north coast received above average rainfall marked by several severe storms
in December, southeastern Brazil, Paraguay and Northern Argentina
experienced drier than average conditions.

Africa: The rainy season in southern Africa
is under way with average rainfall in the west but drier regions in the
eastern Congo and Zambia for the three month period.

Europe and Asia: Rainfall accumulations
have been normal for the season, although Western Europe experienced violent
storms in December.

North America: Except for the Pacific
Northwest, drier than average conditions continued to prevail in
much of the United States.

Middle East: Below average rainfall has persisted
in the early part of the rainy season in Israel, Iraq and Syria.